Flehmen response
The flehmen response (; from German flehmen 'to bare the upper teeth', and Upper Saxon German flemmen 'to look spiteful'), also called the flehmen position, flehmen reaction, flehmen grimace, flehming, or flehmening, is a behavior in which an animal curls back its upper lip exposing its front teeth, inhales with the nostrils usually closed, and then often holds this position for several seconds. The behavior occurs as a response to relevant external stimuli, typically pheromones, which may have been produced by animals of the same or different species.